2.5 s4 PROTEIN pr2 s4 PROTEIN pr1 SQUARE_CLOSEUP_NORTH inactive inactive inactive active inactive cytoplasm transmembrane PROTEIN pr1 inside PROTEIN pr2 transmembrane COMPLEX ligand_slash_receptor_br_complex HETERODIMER_ASSOCIATION 0.4529421069281876,0.4432668986607613 sa2 sa1 csa1